Apparatus for dispersing carbon black in a liquid medium



Feb. 21, 1961 G. L. HELLER APPARATUS FOR DISPERSING CARBON BLACK IN ALIQUID MEDIUM R E 3 0 E T H N E L E H G R O E 6 Original Filed Nov. 18,1953 ATTORNEY A 2,972,473 e. Patented .reh..,z1,.,.1se,1

APPARATUS FOR DISPERSING CARBON BLACK IN A LIQUID MEDIUM George L.Heller, Monroe, La., assignor to 'Columbian Carbon Company, New York,N.Y., a corporation of Delaware Original application Nov. .18, 1953,Ser. No. 392,955. and this application May 21, 1957 Ser. No;

, 4'Claims. (Cl. 259-9) The present invention relates to novel apparatusof particular utility in the agglutinatingof carbon black and natural orsynthetic rubber, or other polymeric materials, and in the continuousproduction of aqueous carbon black slurries adapted for such use, asdescribed and claimed in my copending application Ser. No. 392,955,filed November 18, 1953, now abandoned, of which the present applicationis a division. Carbon black is extensively used as a reinforcing agentin rubber. It has for many years been conventional practice toincorporate the carbon black inthe coagulated rubber by vigorousmilling. This method has proved tedious and costly and, in someinstances, has deleterious- 1y affected the properties of the finishedrubber product More recently, extensive research has been carried on inview of developing a satisfactory, practical method however, that theinvention in its broader aspect is not limited to the particularembodiment thereof shown in the drawings.

,Figure 1 of the drawings is a longitudinal, sectional view of a mixingconduit, showing in elevation apparatus auxiliary thereto;

Figure 2 is atransverse sectional view along the line 2-2 of Figure 1;

Figure 3 is a plan view of'a rotor comprising blades having theirforward edges beveled on their upstream side; a

Figure 4 is a similar view of a rotor comprising blades having theirforward edges beveled on their downstream side; and T Figure 5 is afragmentary viewshowing one means of securing the rotors to therotatably mounted shaft.

Referring more particularly to Figure 1, the mixing conduit consistsofan elongated tubular member 1, closed at its upstream end by thesealing member 2 and closed at its downstream end by the sealing member3. These I sealing members fit into the respective ends of the conduit1, have radially extending flanges 4, and are held in position bymachine bolt 5 and theflanges 6, the latter being securely fastened, asby welding, to the tubular member 1. Leakage between the walls of thetubular 1 member 1 and the sealing members 2 and 3 is prevented ofdispersing carbon black in rubber by mixing the black with the rubberlatex, prior to the coagulation of the rubber. But in most instancesthese efforts have led only to batch operations, requiring the use ofdispersing agents for effecting and maintaining satisfactory dispersionof the carbon black in aqueous slurry form until it can be laterincorporated with the latex. Such operations have been costly withrespect to equipment and .labor, have produced ununiform results, due tolack of uniformity of the carbon black slurry, and the presence of thedispersing agents has deleteriously affected the characteristics of thefinished rubber product. p In view of producing a more uniform slurryfor mixing with the latex, it has been proposed to grind the carbonblack in water. But such procedure has presented serious diflicultiesdue to erosion of the grinding surfaces by the carbon black, and thebinding, plugging and stoppage of the grinding mill. In Patent No.2,769,795 issued on anapplication of Harold A. Braendle, copending withmy above-noted application Ser. No. 392,955, there is described andclaimed an improved process for dispersing carbon black in rubberlatices, which is adapted to continuous operation, and in accordancewith which a stream of uniform aqueous slurry of carbon black isprepared by continuously feeding carbon black and water, inpredetermined proportions, to a mixing chamber and uniformly disparsingthe carbon black in the water stream by violent hydraulic turbulence andimpact. The resultant stream of slurry is then immediately andcontinuously blended with a stream of the latex under conditions ofviolent hydraulic turbulence and impact.

. The apparatus of my present invention-is especially adapted to thecarrying out of the process of said Braen'dle Patent 2,769,795, andespecially the process described and claimed in my said copendingapplication, in large, I

commercial scale operations.

The apparatus of my present invention will be further has been used withparticular. advantage in carryingout the process of my said application.'It willbeunderstood,

by sealing gaskets 7. The shaft 8 extends coaxially through the entirelength of the mixing conduit and is rotatably supported at each end ofthe bearings 9, these hearings being, in turn, secured by machine bolt10 to adjustable brackets 11, fastened to the base platel2 by means ofbolts 13. The shaft is provided at its left-hand end with a pulley14,,oi other suitable means, for connecting the shaft by belt, orotherwise, with an electric motor, or other suitable power source, notshown, for. rotating the 'shaft at high speed. The shaft 8 extendsthrough the sealing members 2 and 3 and is sealed therein againstleakage by means of mechanical shaft seals 15,;hereinafter more fullydescribed, adapted to be held in positon by the end plates 16. Theconduit 1 is supported by brackets 17 which are fastened to the base 12by means of bolts 18. 'l.' "he conduit is provided at its upper sidewith an inlet 19, an outlet 20, and intermediate valved inlets 21 and22, the latterinlets being for the introduction of latex, or othermaterials, as hereinafter more fully described.

Stators 23 project inwardly from the wall of the conduit and are securedthereto-by welding or other suitable means. As will hereinafter appear,thesestators are relatively thin sheets. They are of substantiallygreater length than thickness and are positioned with their broad sidesextending longitudinally of the conduit. Intermedieate these statorsthere are groups of rotors 24, each about one-eighth inch thickextending radially from the shaft .8.' These rotors. may be permanentlyfastened to the shaft as by welding, as shown in Figure 5 of thedrawing, but are,with advantage, welded to collars 25 adapted to bemoved along the shaft, so as to adjust the position of the rotors 24with respect to the stators 23, and held in position by the set-screws26. As more clearly shown in Figures 3 and 4 of the drawing, theserotors 24 are composed of four outwardly ex; tending arms or blades 27on centers spaced apart, each rotor thus comprising a plurality offlatblades of substantial uniform thickness symmetrically spaced about theshaft and lying in a common'plane perpendicular to the longitudinal axisof the shaft. The forward edge of each of these arms is so constructedas toform a knife edge. These knife edges are, with advantage, formed bybeveling one side of the forward edgeof each arm-the other side of theedgesremaining straight. Particular} ly advantageous results have beenobtained where the beveled surfaces of adjacent groups of rotors face inopposite directions, so as to exert opposing propelling action on thestream of slurry passing through the conduit.

It will be understood, however, that the invention contemplates stillother types of rotors, including rotors having a greater or lessernumber of arms and blades having cutting edges beveled equally from eachside, as well as an arrangement of blades of the specific type shownhaving all of the beveled edges facing in'the same direction. But thepreferred arrangement is that shown, as it has been found to give mostsatisfactory results. The invention also contemplates blades havingbothforward and rearward edges sharpened.

I have also found it most advantageous to position the rotors on theshaft so. that the cutting edge of each blade is spaced from thecorresponding cutting edge of the next adjacent blade or blades of thegroup by an angle of about 30. This angle may be varied somewhat but Ihave found that for optimum results an angle of about 30 is mostadvantageous. As to those groups of blades having beveled edges facingdownstream, the leading blade should be on the upstream side, and as tothose groups having their beveled edges facing upstream, the leadingedges should be on the downstream side, as shown more particularly inFigure 2 of the drawing.

The diameter and length of the mixing conduit is subject to somevariation, the optimum dimensions depending on charging rates, rate ofrotation of the blades and number of cutting edges and thecharacteristics of the particular carbon black being processed. I have,with advantage, used mixing conduits of the type shown ranging from 2 to3 feet long and '2 inches, 4 inches and 6 inches in diameter,respectively. With smaller diameters, mechanical difficulties areencountered. The diameter should not be so great as to permit anysubstantial holdup of any of the materials passing therethrough, so

that the rate of discharge of any constituent might differ from the rateof feed.

These blades should be adapted to be rotated at a rate to give a tipvelocity of the order of at least 3,500 feet per minute. With mixingconduits 4 inches in diameter, the blade assembly should be. adapted tobe rotated at about 5600 r.p.m., with a 6 inch conduit, 3600 r.p.m. andwith a 2 inch conduit, 7200 r.p.m.

A mixture of carbon black and water in measured, predeterminedproportions is introduced through the inlet 19 and, while passing as aflowing stream through the conduit, is subjected to the violent impactof the rapidly form mixing before any coagulation of the latex canproceed.

Particularly in the type of operation just described, it is advantageousthat the charging rate with respect to the diameter of the mixingchamber be so correlated as to result in a relatively high linearvelocity of the mixture through the mixing conduit, say of the order ofl to 5 feet per second, and more advantageously, about 4 feet persecond. In order to obtain such high velocities, it is generallynecessary to supply the carbon black-water mixture under considerablepressure and to avoid leakage from the mixing conduit around therotating shaft, special sealing means is frequently necessary. Varioustypes of sealing means, lsuitablefor this purpose, are available, forinstance, various balanced-pressure seals and mechanical seals.

I have, with particular advantage, used a mechanical shaft seal of thetype marketed under. the trade-name Syntron, and shown in Figure 1 ofthe drawings, somewhat enlarged for clarity. This seal is composed ofstationary graphite rings 28, sealed into each end of the members 2 and3 by rubber rings 29. The steel members 30 rotate with the shaft andform a pressure contact with the graphite rings, being forced againstsaid rings by the coil springs 31.acting on the beveled steel members 32and the intervening 'U-shaped rubber rings 33. By this action, therubber rings are forced against the shaft with which they rotate,forming a seal between the rotating elements and the shaft. I have foundit further advantageous to maintain water pressure of about 2 to 5pounds on the chamber within the sealing members 2 and 3, the waterbeing supplied to the chamber through tubes 34. Where the shaft is to besubjected to thrusts, it may be constructed with shoulders 35 adapted tobear on the end plates 16. v

The duration of the agitation of the latex, or other added ingredient,with the slurry can be varied depend- 1 ing'upon whether the latex isintroduced through inlet 21 rotating blades and the violent churningagitation caused by said rotation, while mass rotation of the streamwith the blades is substantially inhibited by the intervening stators.Where the carbon black is introduced in pellet form, this violent impactand shearing action causes rapid disintegration of the pellets anduniform dispersion of the carbon black in the water to produce a uniformstream of carbon black slurry.

According to one aspect of the invention, while this stream of slurry isbeing subjected to this violent agitation, a stream of the latex isintroduced in measured predetermined proportion through the inlet 21 or22, and by reason of the turbulent condition of the flurry stream andcontinued agitation caused by the subsequent rotating blades, the latexis substantially instantaneously, uniformly mixed with the slurry. Theresultant mixture is continuously withdrawn from the mixing conduitthrough the outlet 20 and passed directly to the coagulation tank.

In this procedure, there is no holdup of the carbon black, or any of theother added materials and, therefore, the concentration of carbon black.in the slurry at the point of mixing with the latex is dependent solelyupon the proportions of carbon black and water charged to the system.Further, this slurry is immediately mixed with the latex and, therefore,no settling nor localized concentration of the carbon black can occur,and the mixing of the slurry with the latex is so rapid as to effectunior through inlet 22. Additional intermediate inlets may be provided,where desired, to permit further variation in the duration of thismixing.

I have generally found it mostadvantageous to space the rotors-along theshaft in groups of three with intervening stators. ltwill be noted,however, that such grouping is not essential. Stators maybe placedbetween each pair of rotors, but the additional construction cost is notusually warranted. The rotors may be arranged in groups of more thanthree but, as the number of rotors per group is increased, theredevelops a tendency toward mass rotation of the stream with the groupsof rotors and the severity of'the impact is somewhat lessened.

A particularly effective embodiment of the invention was constructedsubstantially as shown in the drawings, using a piece of standard 6 inchpipe, 31 inches long as the mixing conduit. The shaft was of 2 inch coldrolled steel. Five stators of stainless steel, inch thick, 1 inch highand 3 inches long were welded to the lower inner wall of the conduit soas to project vertically inwardly and spaced apart 1 /2 inches. Sixgroups of rotors, of 3 rotors each, were spaced along the shaft, asshown in the drawings, the rotors of each group being spaced apart Ainch. The clearance between the outer edges of the blades and the innerwall of the conduit was inch. These blades were constructed, as shown inthe drawings, with sharp forward edges, the beveled faces of the bladesof each group opposing those of the adjacent group of blades, in orderto neutralize pumping or propeller action and to cause increasedturbulence. The inlets 19, 21, and 22 were of 1 inch'pipe and the outlet20 was of 1 /2 inch pipe, each welded to the mixing conduit. The centerline of inlet 21 was 16% inches downstream from the center line of inlet19. The distance between center lines of inlet 21 and 22 was 5 inchesand the distance between the center linefof inlet 22 and outlet 20 was3% inches. The leading edgeof each blade was spaced 30 from the leadingedges of the adjacent blade or blades of the group. The blades were Vsinch thick.

It will be understood that these dimensions may be varied somewhat.However, the diameter of the mixing conduit should not be sufi'icientlygreat to interfere with the flowing-stream characteristics, or to permitany separation or localized concentration, of the materials passingtherethrough and the clearances should be sufiiciently great to avoidany grinding or smearing action.

I have, for instance, With advantage, used mixing conduits 4 inches indiameter and 2 inches in diameter. A six inch diameter conduit ispresently preferred because of its greater capacity. But conduits muchin excess of 6 inches in diameter are apt to result in less uniformmixing.

I have found that Where the forward edges of the blades are blunt, toogreat an amount of heat is developed by friction at the necessary highvelocity of the blades, and an excessive amount of work is required toeffect their rotation. Even more important is the tendency of therapidly rotating blades to push the suspension ahead of the bladewithout cutting through the liquid to exert adequate disrupting forceson the carbon black pellets or aggregates to be disintegrated anddispersed. I have further found it advantageous, though not essential,that the rearward edges of the blades also be sharpened, as thisinhibits cavitation and also lessens blade friction and temperaturebuild-up.

It is important to avoid too great a temperature buildup in the mixingconduit, as elevated temperatures tend to accelerate unduly the rate ofcoagulation of the latex when the resultant slurry is mixed therewith.My invention provides apparatus whereby maximum dispersion of the carbonblack is effected without objectionable increase in slurry temperature.

In forming the slurry, it is particularly advantageous to avoid theaddition of any so-called dispersing agent, i.e. agents for aiding inthe dispersion of the black in the water or for stabilizing theresulting suspension. In the absence of such agents, it is importantthat the resultant slurry stream be immediately mixed with the latexbefore any separation, or local concentration, of the black can occur.It is also important that the mixing of the slurry with the latex beexceedingly rapid in order to avoid formation of rubber curds, oraggregates containing excessively large proportions of carbon black,which have been found to be exceedingly difiicult to disperse bysubsequent milling.

In accordance with my present invention, uniform mix ing of the slurrywith the latex may be effected substantially instantaneously bycontinuously charging a stream of latex at a uniform predetermined rateinto a zone of the mixing conduit previously described intermediate itsends and downstream from the zone in which the uniform carbon blackslurry is formed. The mixing is thus rapidly effected by the violentagitation within the mixing conduit and the resultant latex mixture iscontinuously passed from the conduit and immediately coagulated by theadding of acid, or other conventional coagulant, with agitation.

As an alternative, the carbon black slurry may be formed in the mixingconduit and continuously passed therefrom as a stream, and this streamof slurry immediately blended with a stream of the latex, inpredetermined proportions, under conditions of violent turbulence, forinstance, by violent impact of one stream with the other, The resultantmixture is then passed immediately to the coagulating tank andcoagulated, as previously described.

The action of the blades within the mixing conduit is not to be confusedwith a grinding or smearing action. It is essential that the clearancesbetween the rotating blades and the wall of the conduit, and otherstationary parts therein be sufficiently great to avoid grinding orsmearing of the black, as such conditions have been found to result in abuild-up of the black on the solid surfaces, eventually necessitatingdiscontinuing the operation. In the apparatus of my present invention,clearances between moving metal surfaces are not less than about inch,preferably within a range of inch to inch.

I claim:

1. Apparatus for effecting the dispersion of carbon black in a liquidmedium, whereby a uniform stream of the dispersion may be continuouslyproduced, comprising an elongated, tubular conduit of relatively smalland substantially uniform cross-sectional area and a closure member ateach end of said conduit, forming an enclosed mixing chamber adapted tobe maintained under superatmospheric pressure, a rotatably mounted shaftextending coaxially through said conduit, supported by said end-closuremembers and sealed therein against leakage, conduit means adapted to theintroducing of the carbon black and the liquid medium under pressureinto one end of the mixing chamber, an outlet conduit at the oppositeend of the chamber, a plurality of stators spaced apart over the lengthof the chamber, extending inwardly from the Wall thereof, of greaterlength than thickness and positioned with their broad sides extendinglongitudinally of the chamber, a multiplicity of rotors of equaldiameters mounted on the shaft, each rotor comprising a plurality ofradially-extending blades, each about oneeighth inch in thickness overthe major portion of their areas, but having sharp forward edges, theblades of each rotor lying in a plane perpendicular to the longitudinalaxis of the shaft, and the rotors being adapted to rotate with the shaftout of contact with the chamber wall and stators, said rotors beingspaced along the shaft intermediate the respective stators and saidshaft and rotors being adapted to be rotated at a blade-tip velocity ofat least 3500 feet per minute.

2. The apparatus of claim 1 in which the rotors are grouped in multiplesalong the shaft intermediate the respective stators.

3. The apparatus of claim 1 further characterized in that there isprovided at least one conduit opening into the mixing chamber at a pointintermediate the inlet conduit means and the outlet conduit.

4. The apparatus of claim 1 further characterized in that the rotors aregrouped in multiples along the shaft intermediate the respective statorsand the forward edges of the blades of one rotor of a group arecircumferentially spaced from the forward edges of the blades of theadjacent rotor of the group by an angle of about 30.

References Cited in the file of this patent UNITED STATES PATENTS638,743 McLellan Dec. 12, 1899 857,179 Jacolucci June 18, 1907 1,246,003Headley Nov. 6, 1917 1,363,368 Sonsthagen Dec. 28, 1920 1,745,291 BleilJan. 28, 1930 2,507,819 Schneider 2 May 16, 1950 2,804,112 Schaller Aug.27, 1957 FOREIGN PATENTS 689,465 France May 27, 1930

